Developing device for electrostatic charge images

ABSTRACT

A developing device for a carrier provided with electrostatic charge images, consisting of a trough-like chamber which accommodates a paddle wheel. A vertical partition limits a gaplike space in which developing powder is forced upwards by slow rotation of the paddle wheel until it comes into contact with the carrier.

United States Patent [191 Dietz [111 3,823,689 [45] July 16, 1974 DEVELOPING DEVICE FOR ELECTROSTATIC CHARGE IMAGES [75] Inventor: Gerardus Dietz,Rijswijk,

Netherlands [73] Assignee: U.S. Philips Corporation, New

York, NY.

[22] Filed: Sept. 18, 1972 211 Appl. No.: 290,236

[30] Foreign Application Priority Data Sept. 29, 1971 Netherlands 7113329 [52] US. Cl. 118/637, 117/115 [51] Int. Cl G03g 13/00 [58] Field of Search 118/308, 310, 312, 636,

[56] References Cited UNITED STATES PATENTS 3,599,604 8/1971 Chawda 118/637 3,682,137 8/1972 Roth et a1. 118/637 Primary ExaminerR0bert R. Mackey Assistant ExaminerLeo Milstein Attorney, Agent, or Firm-Frank R. Trifari [57] ABSTRACT A developing device for a carrier provided with electrostatic charge images, consisting of a trough-like chamber which accommodates a paddle wheel. A vertical partition limits a gap-like space in which developing powder is forced upwards by slow rotation of the paddle wheel until it comes into contact with the carrier.

5 Claims, 4 Drawing Figures PATENTED U 1 51974 SHEET 2 BF 2 1. DEVELOPING DEVICE FOR ELECTROSTATIC CHARGE IMAGES The invention relates to a device for developing electrostatic charge images which are formed on a carrier, consisting of a trough-like chamber having two sidewalls, a front wall and a rear wall, it being possible to transport the carrier over the upper edge of said front wall in a direction which is perpendicular to said upper edge, the carrier thus covering at least partly the open upper side of the chamber, said chamber being capable of containing a quantity of developing powder which can be putinto motion by means of a paddle wheel, said paddle wheel being rotatable about a shaft which is parallel to the upper edge.

Electrostatic charge images can be formed on a suitable carrier by locally charging the carrier by means of an electrostatic printing head. Another method is the homogeneous charging of a photoconductive carrier, followed by the projection of an image onto the carrier, in which case the charge is depleted at the exposed areas.

After the charge image has been provided, it is developed by bringing the carrier into contact with a developing powder consisting of dye particles and possibly carrier grains. After that, the image is visible-and it can be fixed, for example, by heating the carrienKnown devices for development of the electrostatic charge image generally comprise a chamber with an aperture which is to be closed by the carrier to be developed. During operation a paddle wheel rotates inside the chamber at such a rate that the developing powder forms a cloud which comes into contact with the carrier. An example of such a device is described in U.S. Pat. No. 2,221,776.

A drawback of the known devices is that they function properly only if they contain only a comparatively small quantity of developing powder. Consequently, the developing powder must be often changed or replenished. So as to prevent the powder circulating in the chamber from contaminating the ambient atmosphere, the chamber must be very tightly sealed. Consequently, the changing of the carrier which closes part of the chamber is complicated and time-consuming.

The invention has for its object to eliminte these drawbacks. To this end, the device according to the invention is characterized in that the chamber comprises a partition which is arranged to be substantially vertical and parallel to the said shaft, the said partition limiting a gap-like space, the other limitation of which is formed by the front wall, said gap-like space constituting a connection between the paddle wheel and the location for the part of the carrier which covers the chamber. By making the paddle wheel rotate comparatively slowly, the developing powder is forced upwards in the gaplike space so that it comes into contact with the carrier without being suspended in the air.

It is to be noted that slow upwards forcing of developing powder is known from French Pat. No. 1,207,385. However, in the device described therein, the powder is displaced by two adjacently arranged paddle wheels which rotate in opposite directions, with the result that the dimensions of the chamber are substantially doubled in the transport direction of the carrier. In view of the present efforts to minimize the dimensions of this kind of device, this constitutes a major drawback which is avoided by the device according to the invention.

So as, to stimulate the mixing of the contents of the chamber, the paddle wheel is preferably formed as a cylindrical cage of blades in the form of strips, which extend parallel to the cylinder axis and whose width does not exceed one sixth of the outer diameter of the paddle wheel.

The contact between the carrier and the developing powder can be further improved by using a second gap between the upper edge of the front wall, and a magnet system which is arranged above the first gap-like space and which extends over the entire length thereof, said second gap forming part of the transport path for the carrier to be developed. In that case, the developing powder must not only contain the pigmentation grains, but also grains of a ferromagnetic material, for example, iron powder, so that it is pulled against the carrier by the magnet system. If the carrier is to be changed, interruption of the magnetic attraction is desirable. To this end, the magnet system can be composed of, for example, a number of electromagnets, the 'power supply of which can be interrupted as desired. However, a system of this kind requires additional energy during operation. Consequently, preferance is to be given to a further embodiment of the device wherein the magnet system consists of a cylindrical body which is rotatable about its axis which is parallel to the second gap, said cylindrical body consisting of a permanentaly magnetized material over a portion of its circumference which extends over the entire length of the cylinder. The half of the cylinder which is arranged diametrically opposite to this magnetized portion comprises a screen made ofa material having a magnetically screening action. By rotating the cylinder about its axis, it is achieved that the action of the magnetized portion is screened in the direction'of the carrier so that the developing powder is no longer pulled against the carrier.

The invention will be described in detail with reference to the drawing. Therein:

FIG. 1 is a longitudinal sectional view of an electrostatic printing device comprising a developing device according to the invention, 7

FIG. 2 is a plan view of the printing device shown in FIG. I,

FIG. 3 is a sectional view illustrating the operation of the developing device according to the invention, and

FIG. 4 is alongitudinal sectional view of a magnet system used in the developing device of FIG. 3.

The electrostatic printer which is diagrammatically shown in FIGS. 1 and 2 as an example of the application of'a developing device according to the invention, is designed-for printing characters on a carrier 1 which consists of a strip of paper which is unwound from a supply roller 3, and which is passed by a printing head 5. The printing head 5 comprises a number of needlelike image electrodes 7, which produce a charge image on the carrier 1 in cooperation with a counter electrode 9. The construction and the operation of the printing head 5 are generally known, and are irrelevant for a proper understanding of the present invention. For the sake of brevity, this subject will not be elaborated upon in this context.

After the carrier 1 has passed the printing head 5, it is passed in proximity to a chamber 11 which forms part of a developing device, which will be discussed in detail hereinafter. In this developing device, a pigmentation powder adheres to the carrier 1 at the areas where the carrier is electrostatically charged, with the result that the electrostatic charge image is converted into a visible image.

Subsequently, the carrier 1 is passed over a fixing plate 13, which is electrically heated by means of a heating element 15. This heating causes the pigmentation powder to melt with the result that it permanently adheres to the carrier. This is called the fixation of the image. The printing process is then completed, and the carrier 1 can now be further transported to a folding or cutting device (not shown). 7

The carrier 1 is transported by means of two pairs of rollers 17 and 19, and I7 and 19, respectively. The rollers 17 and 17' are connected to a shaft 21 having a pulley 23, the rollers 19 and 19 being connected to a shaft 25 having a pulley 27. The shafts 21 and 25 are journalled in a frame 29, 29, which also supports the fixation plate 13, and which is connected in a hinged manner to side plates 31 and 31. The shaft 33 of the supply roller 3 is also journal in this frame. Owing to the hinged connection of the frame 29, 29, the transport device ,with the carrier 1 can be swung away from the developing device 11, which substantially facilitates the maintenance of the developing device and the insertion of a new strip of paper. The pulleys 23 and 27 are driven, via a belt, by an electric motor (not shown for the sake of clarity). The developing device (see also FIG. 3) consists of a trough-like chamber 11 having a front wall 35, a rear wall 37, and two sidewalls 39 and 39. The upper edge 41 of the front wall 35 is bent over so as to form a guide for the carrier 1. The chamber 11 contains a quantity of developing powder 43 consisting of, for example, a mixture of iron grains having a grain size of I 150 pm, to which 2 percent by weight of toner powder is added which has a grain size of -15 am, and which adheres to the iron grains. A suitable toner powder is, for example,-the product which is marketed by the firm Philip A. Hunt, Chemical Company, Palisades Park, N.Y., U.S.A., under the name Graph-o- Fax No. l. The developing power 43 can be put into motion by a paddle wheel 45, which is rotatable about a shaft 47 which is journalled in the sidewalls 39 and 39, and which is driven by an electric motor 49. The paddle wheel 45 is formed by a cylindrical cage which is made of blades 51 in the form of strips which radially extend outward from the shaft 47. These strips are preferably straight, but if desired they can also be slightly bent or twisted. The strips 51 do not extend as far as the shaft 47: preferably their width does not exceed one sixth of the diameter of the paddle wheel 45. If they were to extend further, they would divide the chamber 11 into a number of more or less separate compartments. This would make the mixing of the developing powder in the chamber more difficult, than is the case with the present open cage structure. This is of importance, because as a result of the developing process, toner is continuously locally taken up from the developing powder. Consequently, the deteriorated developing powder must be continuously mixed with the supply of fresh developing powder 43 in the chamber 11. In this manner, the filling of the chamber 11 can be continuously used until the percentage oftoner powder has decreased to approximately one. If desired, toner powder can be continuously or periodically added to the developing powder 43, so that the developing powder is each time regenerated.

A partition 53 is approximately vertically arranged in the chamber 11, parallel to the shaft 47. In conjunction with the front wall 35, this partition defines a gap-like space 55 which constitutes a connection between the paddle wheel 45 and the carrier 1. The partition 53 terminates preferably at a small distance from the two sidewalls 39 and 39. Two side partitions 56 and 56' extend parallel to these sidewalls, their height being equal to that of the partition 53; these side partitions connect the latter partition to the front wall 35.

A second gap 57 is present between the upper edge 41 of the front wall and a magnet system 59, which is situated above the gap-like space 55. The width of the gap 57 is adjustable in that the chamber 11 can be tilted about a shaft 54. Adjustment is effected by means of an adjusting screw 58 which is provided underneath the chamber 11. The magnet system 59 (see also FIG. 4) preferably consists of a cylindrical body. It is rotatable about its longitudinal axis which is parallel to the gap 57, by means of a shaft 61' which is journalled in the frame 29, 29. A grip 63 is provided onone end of the shaft 61 for rotating the magnet system. Part of the circumference of the cylinder is occupied over the entire length of the gap 55 by a'rod 63 of a permanently magnetized material, for example, ferrite. The magnetization of the material 63 is such that the generated magnetic field extends into the chamber 11. This can be achieved, for example, by magnetizing the magnet 63 in the radial direction. In FIGS. 3 and 4, the magnetic north pole is denoted by N, and the south pole is denoted by S. The half of the cylinder which is diametrically opposite to the magnet 63, comprises a screen 65 which extends over the entire length of the cylinder, and which is made of a material having a magnetically screening action, for example, permalloy.

The operation of the described developing device is as follows. The carrier 1, provided with an electrostatic charge image by the printing head 5, is transported along the magnet system 59, via the gap 57, by means of the transport rollers 17, 19 and 17', 19'. The carrier then slides over the bent over upper edge 41 of the front wall 35 and along recesses in the two sidewalls 39 and 39'. The carrier 1 completely closes the gap 57 between the magnet system 59 and the upper edge 41. The paddle wheel is driven by the motor 49 in the direction indicated in FIG. 3 (counterclockwise) at a low speed of revolution speed, for example, six revolutions per minute. The blades 51, then force the developing powder 43 upwards in the gap-like space 55. At the top of this space, the forced-up developing powder 43 contacts the carrier 1, at the rear of which the magnet 63 is arranged. The iron particles in the developing powder 43, together with the toner particles which ad here thereto, are thus pulled against the carrier 1. The pigmentation particles then adhere to the electrostatically charged areas of the carrier 1, so that the charge image becomes visible. The powder which is near the ends of the magnet system 59 is not pulled against the carrier 1. This powder drops over the side partitions 56 and 56 into the spaces between these side partitions and the sidewalls 39 and 39, where it can be mixed again with the supply of developing powder. Owing to this construction, no requirements are imposed as regards the sealing between the carrier 1 and the sidewalls 39 and 39'.

Thedeveloping powder 43 which is forced up in the gap-like space is taken along by friction of the carrier 1 to a location where the magnetic field no longer exerts a substantial effect. From there, the-iron particles and the toner particles, which have not been used for developing, drop back into the chamber 11. Therein, they are mixed again with the developing powder 43. The flow direction of the developing powder 43 is denoted in FIG. 3 by a series of arrows 60.

If the paper on the supply roller 3 is exhausted, the carrier 1 must be replaced by a new one. As already described, the frame 29, 29 can be hinged upwards for this purpose so that the carrier 1 becomes free. So as to prevent the magnet 63 from taking along part of the developing powder which would contaminate the surroundings, the magnet system 59 is first turned through 180 about its longitudinal axis by means of the grip 63, so that the screen 65 is situated between the magnet and the carrier 1. As a result, the developing powder 43 drops back into the chamber 11 after which the frame 29, 29' can be tilted upwards without objection.

Even though the foregoing description refers to the use of the developing device according to the invention in a given type of electrostatic printer, it is obvious that the device can cooperate equally successfully with other apparatus producing a carrier with an electrostatic charge image. For example, use can also be made of an intermediate carrier on which the charge image is provided and developed, after which the developed image is transferred to an ultimate carrier. It is alternatively possible to provide the charge image on the carrier in many ways other than by means of the electrostatic printing head 5, for example, by projecting an image onto an homogeneously charged photoconductive carrier.

What is claimed is:

l. A device for developing electrostatic charge images which are formed on a carrier, comprising:

a rotably supported paddle wheel for mixing and passing developing powder over a charged image surface of said carrier;

a trough-like chamber containing said paddle wheel, said trough-like chamber comprising a front wall with an upper edge portion, a rear wall, side portions, and a bottom portion joining said front and rear walls and said side portions;

a quantity of developing powder in said bottom portion thereof;

a partition disposed in said chamber in proximity to a peripheral edge of said paddle wheel, said partition defining a conduit in conjunction with said front wall and said side portions of said chamber to conduct said developing powder into contact with said carrier; and guide means supported at an upper end of said conduit for guiding said carrier along a path over said upper edge portion and over an open upper portion of said trough-like chamber, said guide means defining a bend in said path directing said carrier upward away from said bottom portion over the upper end of said conduit, whereby the carrier is brought into contact with said developing powder in the region of, and just beyond, said bend, and excess developing powder falls back into said trough-like chamber.

2. The developing device of claim 1, wherein said guide means comprises said curved upper edge portion of said chamber, and a rotably supported cylinder disposed aboveand in close proximity to said edge portion so as to form a guiding gap therebetween for said carrier to pass therethrough.

3. The developing device of claim 1 wherein said paddle wheel comprises a cylindrical cage having blade-like paddle members radially extending outwardly from a center of said cage, said paddle members having a maximum width of one sixth of an outer diameter of the paddle wheel, the central region of said cage defined by radially inwardly directed edges of said blades being open to free movement of said developing powder.

4. The developing device of claim 2, wherein said developing powder contains iron particles and said guide cylinder-provides a magnetic field to attract the iron in said developing powder, and thus attract said developing powder into contact with said imaged charged carrier as it passes through said guiding gap formed by said guide cylinder and the upper edge of said chamber.

5. The developing device of claim 2 comprising, in addition:

pivotal support means for said trough-like chamber,

said pivotal support means being spaced from said edge portion; and

adjusting means to pivot said trough-like chamber to vary the distance between said edge portion and said rotatably supported cylinder and thereby the width of said guiding gap. 

1. A device for developing electrostatic charge images which are formed on a carrier, comprising: a rotably supported paddle wheel for mixing and passing developing powder over a charged image surface of said carrier; a trough-like chamber containing said paddle wheel, said trough-like chamber comprising a front wall with an upper edge portion, a rear wall, side portions, and a bottom portion joining said front and rear walls and said side portions; a quantity of developing powder in said bottom portion thereof; a partition disposed in said chamber in proximity to a peripheral edge of said paddle wheel, said partition defining a conduit in conjunction with said front wall and said side portions of said chamber to conduct said developing powder into contact with said carrier; and guide means supported at an upper end of said conduit for guiding said carrier along a path over said upper edge portion and over an open upper portion of said trough-like chamber, said guide means defining a bend in said path directing said carrier upward away from said bottom portion over the upper end of said conduit, whereby the carrier is brought into contact with said developing powder in the region of, and just beyond, said bend, and excess developing powder falls back into said trough-like chamber.
 2. The developing device of claim 1, wherein said guide means comprises said curved upper edge portion of said chamber, and a rotably supported cylinder disposed above and in close proximity to said edge portion so as to form a guiding gap therebetween for said carrier to pass therethrough.
 3. The developing device of claim 1 wherein said paddle wheel comprises a cylindrical cage having blade-like paddle members radially extending outwardly from a center of said cage, said paddle members having a maximum width of one sixth of an outer diameter of the paddle wheel, the central region of said cage defined by radially inwardly directed edges of said blades being open to free movement of said developing powder.
 4. The developing device of claim 2, wherein said developing powder contains iron particles and said guide cylinder provides a magnetic field to attract the iron in said developing powder, and thus attract said developing powder into contact with said imaged charged carrier as it passes through said guiding gap formed by said guide cylinder and the upper edge of said chamber.
 5. The developing device of claim 2 comprising, in addition: pivotal support means for said trough-like chamber, said pivotal support means being spaced from said edge portion; and adjusting means to pivot said trough-like chamber to vary the distance between said edge portion and said rotatably supported cylinder and thereby the width of said guiding gap. 